Palmer stated in his book that Sodium from 70 to 150ppm would increase the perception of sweetness in the beer as long as SO4 is kept low. How the experts here think about that?
I was planning to add some baking soda to get about 120ppm of Na for that purpose (all other minerals under check, low sulfate, good PH), decided to ask here before I ruin my batch

Table salt is often used as a sweetener in cooking but I believe it is the chloride that does this. A simple experiment for you to try would be to take two glasses of some light beer and add a pinch of NaCl to one and of CaCl2 to the other or I suppose you could skip the first one. If the CaCl2 has any sweetening effect then it's for sure the chloride. Think I'll go try this myself. It's pretty close to beer o'clock around here.

Do yourself a favor and forget that you ever heard about this chloride sulfate ratio thing. The effects of chloride and sulfate are not antipodal. Each has its own effects. One does not offset the other. You'll make better beer if you understand what these separate effects are and learn how to make them work for you.

I'm not inclined to advocate that a sodium level in the 70 to 150 range will enhance sweetness to a significant degree. I do find that sodium at more moderate level can help with that perception. I'd suggest restricting the sodium level to the 25 to 50 ppm range to help avoid any roughness that can develop as the sodium level rises.

As AJ says, don't think that applying a sulfate/chloride ratio is the answer. The absolute levels of those ions has a much more profound effect on beer flavor than their ratio. You can really screw up beer flavor by blindly following that ratio guff.

If you've ever had a beer with a slight saltiness to it (I recently somehow or another accidentally made one, even though I didn't use salt) then you'll end up rather opposed to any use of NaCl. It's pretty awful.

Just noticed that OP is proposing the use of sodium bicarbonate as a source of sodium. In the first place as I indicate it is the chloride ion you want (best source: calcium chloride) but more to the point you never want to add bicarbonate to brewing water as it raises alkalinity. Use of bicarb has much more potential to ruin the beer than adding the same amount of sodium from sodium chloride.